INDIANAPOLIS, Ind. — To combat the march of weeds trying to overtake crops for sunlight and nutrients, one Nebraska expert advises growers to change it up – that is, alter their fighting style every year, or at least every other year.

And Clint Einspahr is an award-winning combatant. Syngenta named him one of its two Resistance Fighters of the Year for 2011, a yearly recognition of growers who “serve as role models and provide growers with guidance they need to manage weeds successfully.”

Mixing and changing practices is vital to keeping weeds from getting a foothold, said Einspahr, who is a farm marketer for Cargill in southern Nebraska. He was a featured speaker at last week’s 21st National No-Tillage Conference in Indianapolis, which drew nearly 1,200 people, including from other countries.

One thing he does, and advises others to do, is change the herbicide structure he uses every year. It’s not that a farmer needs brand-new chemicals every year; they need to use what they depend on in different ways.

“I’m just using a different style of chemical for the same anchor,” he explained, preaching herbicide diversity.

Another practice gaining popularity is cover-cropping, which he has been using the last couple of years to break up wheat-corn-soybean rotations. Radishes, turnips, ryegrass – “It’s been a really big deal for us to put cover crops in the area, and it’s working for us,” he said.

The University of Illinois Department of Crop Sciences has also recently worked with cover crops to fight weeds, according to Dr. Aaron Hager, associate professor – especially waterhemp, which he said is now found in nearly every Illinois county, if not every one.

One practice researchers have been trying is planting cereal rye and letting it overwinter to grow as long as it can into the spring before burndown for crop planting, so the rye will keep the soil surface covered and shielded from sun and nutrients important for early weed growth. Einspahr also advises growers mix multiple species with the rye and keep foliage thick.

But herbicides are important to no-till systems too, both said. Hager showed a slide to his audience of a large field rampant with tall weeds, to illustrate the severity of the problem, saying, “Yes, there are actually soybeans planted in that field; you just can’t see them.”

That photo was taken in 2007; he showed the field in 2010, and it appeared neat and tidy with just crops. Hager said the farmer had changed his weed resistance practices, including applying full-rate herbicide within seven days before or three days after planting beginning in 2008. Post-emergent application was made before waterhemp could reach a height of 3-5 inches.

“We did not do a very good job on my side, of selling you guys full-rate (herbicides),” Einspahr added. “It was easier to sell half-rate.”

Hager said he recognizes farmers are limited in their weed-fighting tools with herbicide, since there are no new active ingredients on the immediate horizon from research; this is why Einspahr advises his growers to juggle their combinations and applications.

In his region, kochia is the No. 1 weed threat. In Illinois, it’s waterhemp, but Hager said Palmer amaranth is spreading across the state as well. The native southwestern U.S. weed has also recently been sighted in northwestern Indiana and parts of Michigan.

“This is the outcome of simplified weed control,” Hager warned of relying on just one chemical or practice for too long, “and it’s not good.” He pointed out biological systems change over time, and will adapt to something that is constant and unchanging – such as a practice.

A third suggestion to interrupt the lifecycle of weeds that Hager put forth comes from the University of Arkansas. He said its agronomy program adopted a “zero tolerance” policy for Palmer (which is particularly thick in the South) – if any of it is spotted in a field, no matter how little, it is removed immediately.

Hager said every grower has stood on the edge of a field and spotted “that one weed” way out in the middle that seems to be alone and “not hurting anything” – it’s a pain to trudge out to examine and pull it, so many won’t. But, he pointed out, that’s exactly what the Arkansas researchers are doing. Just one female Palmer plant, he said, can produce hundreds of thousands of seeds.

Einspahr said in his area, no-tillers are slowing the growth of kochia by not disturbing the ground more than necessary, to keep as many seeds from the weed scattered on top of the ground instead of plowing them under to access soil nutrients.